Here is what I do in your situation:
Start LiveTV. When you get the message the input is in use, hit the escape button and get to the mythtv menu. If you are quick and navigate to Library->Recordings and move the cursor to a recording (you don't have to start it), then the popups saying that the input is in use will stop and you'll be able to freely do what you need to do. You have to be pretty quick though and get this done before the next popup!
Also, if you're just doing it to manage recording schedules, I'd recommend using mythweb (192.168.80.1/mythweb). Its got a great interface for managing recording schedules, and is all I use now.